Ryan Ellis, 33, formerly of Greenbush and Dover-Foxcroft, pleaded guilty to one count each of conspiracy to possess with the intent to distribute and conspiracy to distribute MDPV, a chemical compound commonly referred to as “bath salts” or “monkey dust,” and to possession of firearms during and in relation to a drug trafficking offense, according to a press release issued Wednesday by the U.S. Attorney’s Office.

Earlier this year, Jim Pease, special agent supervisor for the Maine Drug Enforcement Agency’s midcoast regional task force, referred to Ellis as one of the “fathers” of the bath salts problem in Bangor and midcoast Maine.

A sentencing date for Ellis has not been set.

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Ellis and 13 others were indicted by a federal grand jury in July 2013 in connection with an alleged conspiracy to distribute MDPV in 2011. The drug is known to cause paranoia, convulsions and psychotic behavior in users.

The number of defendants indicted appears to make this the largest bath salts conspiracy case prosecuted by the U.S. Attorney’s Office in Maine.

By pleading guilty, Ellis, who was also known as “Dude,” “Calvin” or “Piles,” admitted that between April and December 2011, he and other members of the conspiracy illegally distributed large quantities of MDPV in Penobscot, Aroostook and Knox counties, the press release said. The defendant obtained bath salts from other conspirators, processed and repackaged it, and distributed it to other conspirators for sale to drug addicts.

Ellis was living and working in Piscataquis County when he was arrested on the federal charge in August 2013, according to a previously published report. He was on community release from the Charleston Correctional Facility serving a three-year state sentence on a drug charge when he was indicted on the federal charges.

He chose to return to the state prison to complete his sentence on the state charge rather than be held without bail while awaiting the resolution of the federal charges. Ellis last month was ordered held without bail on the federal charges after he was released from state prison.

In exchange for his guilty plea, federal prosecutors will drop two charges, using or maintaining a drug-involved residence and unlawful use of a controlled substance, when Ellis is sentenced. He also agreed to waive his right to appeal to the 1st U.S. Circuit Court of Appeals in Boston if his sentence is longer than 10 years. He faces up to 20 years in prison and a fine of up to $1 million. Ellis faces a mandatory minimum sentence of five years, which must be served consecutively to the drug sentence, and a fine of up to $250,000 on the gun charge.

Although similar behavior appears to have led to Ellis being charged in state court in 2011 and federal court in 2013, the constitutional guarantee against double jeopardy does not apply, because the charges are not the same and were lodged under different jurisdictions — one state, the other federal.

Others charged in the case include Adam Hathorn, 36, of Bangor; Tina “Fumble” Keaton, 32, of Bangor; Michael “Bub” Tardiff, 53, of Old Town; Matthew Tardiff, 27, of Old Town; Steven Orosco, 23, of Orrington; Jessica Bryden, 21, of Greenbush; Daniel Hines, 37, of Orrington; Alan Ketchen, 40, also known as “AJ” or “Hobbes,” of Bangor; Jacob Gagnon, 25, of Van Buren, formerly of Bangor, also known as “Jake the Snake”; April Kane, 28, of Gorham; Elizabeth Mikotowicz, 27, of Bangor; Jamie Lewis, 37, formerly of Bangor, now of New Hampshire; and Gina Nelson, 30, of Bradley.

All but Gagnon, Kane and Lewis have pleaded guilty. Gagnon and Kane are scheduled to plead guilty later this month. Lewis is tentatively scheduled to be tried next month.